1. Field of the Invention
The invention concerns selective electrolytic deposition of a metal onto the inside surface of bush type hollow bodies, more particularly onto the inside surface of connector contact members, i.e., metal parts mounted on an insulative support which provide the electrical connection between the male and female halves of the connector.
If the metal to be deposited is a costly noble metal such as gold, it is advantageous to deposit it only onto the functional areas of the part, rather than over all of the part. In the case of a connector, these functional areas are the surfaces at which there is mechanical and electrical contact between the male and female members.
In the case of female contacts in particular, it is advantageous to coat the contact only on its inside surface, which is its functional surface.
In the specific case of female contacts which exhibit symmetry of revolution or like members such as bushes, as distinct from flat contacts such as lyre shape or lip type contacts, to which other coating techniques are appropriate, a method for selectively coating the inside surface only of the bush has already been proposed.
2. Description of the Prior Art
This known process is disclosed in EP-A-0 091 209 and in a number of later applications including WO-A-88/04699. It entails inserting an axial anode into the bush, injecting the electrolyte into the interior cavity of the bush and passing current between the axial anode and the body of the bush which forms the cathode of the electrolysis cell; injection is carried out in such a way that the electrolyte comes into contact with the axial anode inserted into the bush and with the interior wall of the bush.
This technique is effective for selective gold-plating of the inside surface of the bush, but there are problems, in particular:
it is difficult to position and center the axial anode, especially in the case of bushes with a small inside diameter: it is essential for the anode not to touch the walls of the bush (which would cause a short-circuit in the electrolysis circuit) and for the accuracy of the concentricity of the anode and the bush to be sufficiently high to enable harmonious distribution of current flow between the anode and the cathode in order to obtain a regular deposit of metal on the walls of the bush; PA1 insertion of the anode into the bush implies a reciprocating movement which seriously reduces production throughput and increases the risk of loss of adjustment and breakdowns, due to the large number of moving parts which have to be reciprocated; PA1 finally, this technique is restricted to small depths of penetration as the previous two problems quickly become insurmountable as the depth of insertion of the anode in the bush increases. PA1 a) positioning the bush to face a system comprising an injector nozzle and a suction nozzle concentric with and of greater diameter than the injector nozzle, the system being so configured that the bush, the injector nozzle and the suction nozzle are aligned, that the injector nozzle does not enter the bush and that a peripheral gap remains between the bush and the suction nozzle, and PA1 b) simultaneously: PA1 b1) injecting into the interior volume of the bush via the injector nozzle a liquid electrolyte charged with a salt of the metal to be deposited so that the liquid electrolyte wets the walls of the interior volume of the bush, and PA1 b2) passing an electric current between the bush and an electrode in electrical contact with the liquid on the output side of the injector nozzle to cause deposition of said metal on said walls of the interior volume of the bush wetted by said liquid injected by the injector nozzle. PA1 at least one system comprising an injector nozzle and a suction nozzle which are substantially coaxial, the suction nozzle having a diameter greater than that of the injector nozzle, PA1 means for placing each bush to be plated facing a system so that the bush, the injector nozzle and the suction nozzle are in alignment, so that the injector nozzle does not enter the bush and so that a peripheral gap remains between the bush and said suction nozzle, PA1 means for injecting via the injector nozzle a liquid electrolyte charged with a salt of the metal to be deposited, PA1 an electrode in electrical contact with the liquid electrolyte on the exit side of the injector nozzle, and PA1 means for passing an electric current between the bush and said electrode. PA1 a hollow first plate defining a first circular chamber connected at the center to the injector means and discharging at the periphery via a plurality of the injector nozzles which are parallel and oriented in the axial direction, PA1 a hollow second plate defining a circular second chamber connected at the center to the suction means and discharging at the periphery via a plurality of the suction nozzles which are oriented in the axial direction, the injector nozzles projecting from the first plate passing through the second plate so that each injector nozzle discharges substantially in the vicinity of a corresponding suction nozzle, and PA1 a third plate with means for guiding bushes fed successively and continuously to the machine adapted to move said bushes past said suction nozzles of said second plate.
One object of the invention is to remedy these drawbacks by proposing a gold-plating process (more generally, an electrolytic process of depositing a metal such as a noble metal) which restricts the electrolytic deposit to the inside surface only of a bush without requiring the insertion of an anode into the bush.
It will be shown that no reciprocating movement is necessary, and in this way the invention can significantly increase production throughput and the accuracy of centering and therefore the regularity of the gold-plating thickness.
Finally, it will be shown that the method of the invention can gold-plate the inside surface of the bush to a depth which is significantly greater than in the prior art without comprising the accuracy of the operation or the throughput.
The invention concerns only hollow parts with symmetry of revolution, such as bushes, but is applicable to all parts of this type, regardless of whether the bushes are manufactured by turning or by cutting and rolling in the case of female contact members.